It has been common to employ the swaging process in the case of forming metal pipes to a desired shape. For example, the baseball bat made of metal has been also gained by forming a metal pipe of aluminium alloy to the shape of bat by the swaging process. However, even if a metal pipe having an excellent property as to its hardness, tension or the like is employed to enhance the performance of the bat formed, the conventional swaging process in which the formation of the bat is attained by moving the upper and lower dies in the upper and the lower directions in a high speed has deteriorated the alloy structure of the metal pipe, causing the metal bat thus formed to be cracked or broken during the use thereof in baseball play. Further, although it is desired that the baseball bat made of metal pipe is formed to have a thick wall at its larger diameter at which a ball is to be hit and a thin wall at its smaller diameter or grip portion, the swaging process has been liable to make the larger diameter portion thin and the grip portion thick and this can be said to be a drawback inherent to the swaging process. Furthermore, the metal baseball bat formed by the conventional process has its grip end formed by welding a different grip end to the grip portion of the bat, thus causing the welded grip end to come off in baseball play, which was very dangerous to the players.